Procedures for ophthalmic laser surgery rely on a phenomenon generally known as Laser Induced Optical Breakdown (LIOB). Specifically, LIOB occurs when a laser pulse is focused to concentrate its energy at a focal point in the tissue that is to be altered. This alteration by LIOB will typically involve the vaporization of tissue and, if uncontrolled, can include unacceptable levels of adverse side effects such as the charring and tearing of the tissue. Obviously, the control of LIOB during a laser surgical procedure is a major concern. One solution for controlling LIOB has been to generate a pulsed laser beam wherein each pulse has a very short duration (e.g. several femtoseconds), and a relatively low, but efficacious, energy level (e.g. 1.5 μJ). For example, U.S. Pat. No. 7,103,077, which issued to Schuhmacher et al. for an invention entitled “System and Method for Measuring and Controlling an Energy of an Ultra-Short Pulse of a Laser Beam,” and which is assigned to the same assignee as the present invention, discloses a system and method for controlling energy levels in a pulsed laser beam. In addition to control over LIOB, an effective surgical procedure also requires precise control over the location and movement of laser focal points in the treatment area.
Although presently available laser surgical systems are capable of controlling pulse energy while rapidly pulsing a laser beam, and although they are also capable of moving the focal point relatively rapidly through the tissue to be altered by LIOB, present procedures are still somewhat time consuming. Time, however, is an important consideration; primarily because the patient's eye must remain stabilized during the entire procedure. Consequently, it is desirable to accomplish laser ophthalmic surgery in the shortest possible time. The creation of a larger focal point with greater energy may possibly shorten the time required for surgery but, due to the increased risk for adverse side effects, this solution may be inappropriate or impractical. Perhaps a more appropriate solution is to move the focal point at a faster rate through the tissue. This solution, however, may also be impractical due to mechanical limitations of the laser beam delivery system. Another solution is to simultaneously operate with a plurality of focal points.
U.S. Pat. No. 6,610,050, which issued to Bille for an invention entitled “Laser Beam Delivery System with Multiple Focal Points” (hereinafter the '050 Patent), and which is assigned to the same assignee as the present invention, discloses the use of multiple focal points for ophthalmic laser surgery. In addition to the size of each focal point, and their operational energy levels, the '050 Patent also considers the separation of the focal points as an important operational concern. Once multiple focal points have been established, however, there is still a question as to how they are to be moved. For instance, it is known that a grating (i.e. beam splitter) can be used to very easily split a single laser beam into a plurality of focal points. Regardless how the laser beam may be moved, however, if the grating remains stationary, the resultant pattern will always have the same orientation. For several applications, this may be unacceptable. In particular, this will be so when it is desirable to move the pattern of focal points along a curved path, such as in a spiral path.
In light of the above it is an object of the present invention to provide a system for performing ophthalmic laser surgery that coordinates the orientation of a focal point pattern with its movement through a tissue treatment area. Another object of the present invention is to provide a system for performing ophthalmic laser surgery that maintains a substantially constant focal point density as a pattern of focal points is moved through a tissue treatment area. Still another object of the present invention is to provide a system for performing ophthalmic laser surgery that reduces the time required for performing laser surgery by simultaneously performing LIOB at a plurality of focal points. Yet another object of the present invention is to provide a system for performing ophthalmic laser surgery that is particularly efficacious for creating a flap of corneal tissue. Another object of the present invention is to provide a system and a method for performing ophthalmic laser surgery that is easy to implement, is simple to use, and is comparatively cost effective.